KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 251 insertions, 0 deletions

diff --git a/tools/debugging/Makefile b/tools/debugging/Makefile
new file mode 100644
index 000000000..e2b7c1a6f
--- /dev/null
+++ b/tools/debugging/Makefile
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for debugging tools
+
+PREFIX ?= /usr
+BINDIR ?= bin
+INSTALL ?= install
+
+TARGET = kernel-chktaint
+
+all: $(TARGET)
+
+clean:
+
+install: kernel-chktaint
+	$(INSTALL) -D -m 755 $(TARGET) $(DESTDIR)$(PREFIX)/$(BINDIR)/$(TARGET)
+
diff --git a/tools/debugging/kernel-chktaint b/tools/debugging/kernel-chktaint
new file mode 100755
index 000000000..e1571c04a
--- /dev/null
+++ b/tools/debugging/kernel-chktaint
@@ -0,0 +1,235 @@
+#! /bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Randy Dunlap <rdunlap@infradead.org>, 2018
+# Thorsten Leemhuis <linux@leemhuis.info>, 2018
+
+usage()
+{
+	cat <<EOF
+usage: ${0##*/}
+       ${0##*/} <int>
+
+Call without parameters to decode /proc/sys/kernel/tainted.
+
+Call with a positive integer as parameter to decode a value you
+retrieved from /proc/sys/kernel/tainted on another system.
+
+EOF
+}
+
+if [ "$1"x != "x" ]; then
+	if  [ "$1"x == "--helpx" ] || [ "$1"x == "-hx" ] ; then
+		usage
+		exit 1
+	elif  [ $1 -ge 0 ] 2>/dev/null ; then
+		taint=$1
+	else
+		echo "Error: Parameter '$1' not a positive integer. Aborting." >&2
+		exit 1
+	fi
+else
+	TAINTFILE="/proc/sys/kernel/tainted"
+	if [ ! -r $TAINTFILE ]; then
+		echo "No file: $TAINTFILE"
+		exit
+	fi
+
+	taint=`cat $TAINTFILE`
+fi
+
+if [ $taint -eq 0 ]; then
+	echo "Kernel not Tainted"
+	exit
+else
+	echo "Kernel is \"tainted\" for the following reasons:"
+fi
+
+T=$taint
+out=
+
+addout() {
+	out=$out$1
+}
+
+if [ `expr $T % 2` -eq 0 ]; then
+	addout "G"
+else
+	addout "P"
+	echo " * proprietary module was loaded (#0)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "F"
+	echo " * module was force loaded (#1)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "S"
+	echo " * kernel running on an out of specification system (#2)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "R"
+	echo " * module was force unloaded (#3)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "M"
+	echo " * processor reported a Machine Check Exception (MCE) (#4)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "B"
+	echo " * bad page referenced or some unexpected page flags (#5)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "U"
+	echo " * taint requested by userspace application (#6)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "D"
+	echo " * kernel died recently, i.e. there was an OOPS or BUG (#7)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "A"
+	echo " * an ACPI table was overridden by user (#8)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "W"
+	echo " * kernel issued warning (#9)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "C"
+	echo " * staging driver was loaded (#10)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "I"
+	echo " * workaround for bug in platform firmware applied (#11)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "O"
+	echo " * externally-built ('out-of-tree') module was loaded  (#12)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "E"
+	echo " * unsigned module was loaded (#13)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "L"
+	echo " * soft lockup occurred (#14)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "K"
+	echo " * kernel has been live patched (#15)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "X"
+	echo " * auxiliary taint, defined for and used by distros (#16)"
+
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "T"
+	echo " * kernel was built with the struct randomization plugin (#17)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "N"
+	echo " * an in-kernel test (such as a KUnit test) has been run (#18)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "J"
+	echo " * fwctl's mutating debug interface was used (#19)"
+fi
+echo "Raw taint value as int/string: $taint/'$out'"
+
+# report on any tainted loadable modules
+[ "$1" = "" ] && [ -r /sys/module/ ] && \
+	cnt=`grep [A-Z] /sys/module/*/taint | wc -l` || cnt=0
+
+if [ $cnt -ne 0 ]; then
+	echo
+	echo "Tainted modules:"
+	for dir in `ls /sys/module` ; do
+		if [ -r /sys/module/$dir/taint ]; then
+			modtnt=`cat /sys/module/$dir/taint`
+			[ "$modtnt" = "" ] || echo " * $dir ($modtnt)"
+		fi
+	done
+fi
+
+echo
+echo "For a more detailed explanation of the various taint flags see"
+echo " Documentation/admin-guide/tainted-kernels.rst in the Linux kernel sources"
+echo " or https://kernel.org/doc/html/latest/admin-guide/tainted-kernels.html"
+#EOF#